Hyatt.] 146 [March 5, 



reproductive zoons in this layer may be a secondary result of ad- 

 aptation, or may have a primitive and hereditary meaning, but of 

 this there seems at present no solution. Their presence, however, 

 gives to this layer an apparent complexity, which is puzzling until 

 one notices that the mesenchyme contains elements, which in 

 higher animals are more completely localized in other layers and 

 in distinct organs. This polymorphism of the cells is really a gen- 

 eralized characteristic which is in strong contrast with the highly 

 specialized uniformity of the flat epithelium of the ectoderm, and 

 the intermediate condition of the endoderm in the Sycones, Leu- 

 cones and Carneospongiae, as shown by the flat epithelium of the 

 archenteron, and the collar cells of the ampullae. 1 

 .The spermatocyst in the mesenchyme of Porifera is like a single 

 wandering cell or any other cell of the tissues, an autotemnon, but 

 it becomes confined in an envelope within which it undergoes 

 spontaneous fission, and the zoons produced possess sufficient 

 resemblance to true monads to have justified Oken and other 

 authors, in considering them as actually monads. 2 They are, 

 however, morphologically, forms of secondary origin, which have 

 these characteristics developed at an early stage of growth. Their 

 ordinary form and structureless body remind one very forcibly of 

 the simple form of cell as figured by Frommann, in his Struct, 

 etc., Zellen, pi. 1, fig. 1, and their development and subsequent 

 histoiy prove that they are nuclear in origin and affinity. 



Whether they do or do not take food seems to us to have no 

 bearing upon the facts of morphology, and to be a question of adap- 

 tation to surroundings. The essential difference between them 

 and flagellate Protozoa is, that they, though structurally young 

 forms when compared with the more highly organized adults of the 

 Flagellata, or even with the cell from which they originated, have 

 already acquired the habits of full grown males or microgonids among 



1 Accordingto Roux "Kampf der Theile im Organismus" this would be the result of 

 natural selection acting upon the cells : this may be true in part, but the origin of the 

 epithelial form may be due to pressure, the origin of the ampullaceous form also to 

 pressure and excess of growth, the origin of the collar and cilia to heredity purely, its 

 preservation to continuance of similar conditions and natural selection be only a sec- 

 ondary influence. 



2 In this connection it is very interesting to read the comparisons of Nussbaum 

 (Archiv. Mikr. Anat., Vol.xvm, p.l) and their conformation by A. Swaen and H.Mas- 

 quelin (Archiv. de Biologie, Vol. iv, p. 797) upon the structure of the testicular and ova- 

 rian envelopes and the development of the spermatocysts and ova. 



